Requirements regarding audio power and audio fidelity of modern speakers and home theater systems are always increasing. At the core of these systems is the power amp. Today's audio amplifiers have to perform well enough to satisfy those always growing requirements. There is a huge amount of amp styles and models. All of these vary when it comes to performance. I am going to describe a few of the most widespread amplifier terms such as "class-A", "class-D" and "t amps" to help you figure out which of these amps is best for your application. In addition, after reading this essay you should be able to understand the amp specs which suppliers publish.
Simply put, the principle of an audio amplifier is to translate a low-power music signal into a high-power audio signal. The high-power signal is great enough to drive a speaker sufficiently loud. To do that, an amp uses one or several elements which are controlled by the low-power signal to generate a large-power signal. These elements range from tubes, bipolar transistors to FET transistors.
Furthermore, tube amplifiers have quite small power efficiency and as a result dissipate a lot of power as heat. Yet an additional disadvantage is the high price tag of tubes. This has put tube amplifiers out of the ballpark for many consumer devices. Consequently, the bulk of audio products nowadays employs solid state amps. I am going to explain solid state amplifiers in the subsequent paragraphs.
A different downside of tube amplifiers, however, is the small power efficiency. The bulk of power which tube amplifiers use up is being dissipated as heat and only a portion is being converted into audio power. Also, tubes are fairly costly to build. Hence tube amplifiers have generally been replaced by solid-state amplifiers which I will glance at next.
To improve on the small efficiency of class-A amps, class-AB amps utilize a series of transistors that each amplify a separate area, each of which being more efficient than class-A amplifiers. The larger efficiency of class-AB amplifiers also has two further benefits. Firstly, the necessary amount of heat sinking is minimized. Consequently class-AB amplifiers can be made lighter and smaller. For that reason, class-AB amps can be made cheaper than class-A amps. When the signal transitions between the two separate regions, though, some amount of distortion is being created, thereby class-AB amplifiers will not achieve the same audio fidelity as class-A amplifiers.
Class-D amplifiers are able to attain power efficiencies higher than 90% by using a switching transistor which is constantly being switched on and off and as a result the transistor itself does not dissipate any heat. The switching transistor, which is being controlled by a pulse-width modulator generates a high-frequency switching component which has to be removed from the amplified signal by utilizing a lowpass filter. Due to non-linearities of the pulse-width modulator and the switching transistor itself, class-D amps by nature have amongst the largest audio distortion of any audio amp.
Class-D amplifiers are able to achieve power efficiencies higher than 90% by making use of a switching transistor that is continually being switched on and off and as a result the transistor itself does not dissipate any heat. The on-off switching times of the transistor are being controlled by a pulse-with modulator (PWM). Usual switching frequencies are in the range of 300 kHz and 1 MHz. This high-frequency switching signal has to be removed from the amplified signal by a lowpass filter. Typically a straightforward first-order lowpass is being utilized. Both the pulse-width modulator and the transistor have non-linearities that result in class-D amplifiers having larger music distortion than other kinds of amps. More recent audio amps incorporate some type of means to reduce distortion. One method is to feed back the amplified audio signal to the input of the amplifier to compare with the original signal. The difference signal is then used in order to correct the switching stage and compensate for the nonlinearity. One type of audio amplifiers which uses this type of feedback is called "class-T" or "t amp". Class-T amplifiers feed back the high-level switching signal to the audio signal processor for comparison. These amplifiers have small music distortion and can be made extremely small.
Simply put, the principle of an audio amplifier is to translate a low-power music signal into a high-power audio signal. The high-power signal is great enough to drive a speaker sufficiently loud. To do that, an amp uses one or several elements which are controlled by the low-power signal to generate a large-power signal. These elements range from tubes, bipolar transistors to FET transistors.
Furthermore, tube amplifiers have quite small power efficiency and as a result dissipate a lot of power as heat. Yet an additional disadvantage is the high price tag of tubes. This has put tube amplifiers out of the ballpark for many consumer devices. Consequently, the bulk of audio products nowadays employs solid state amps. I am going to explain solid state amplifiers in the subsequent paragraphs.
A different downside of tube amplifiers, however, is the small power efficiency. The bulk of power which tube amplifiers use up is being dissipated as heat and only a portion is being converted into audio power. Also, tubes are fairly costly to build. Hence tube amplifiers have generally been replaced by solid-state amplifiers which I will glance at next.
To improve on the small efficiency of class-A amps, class-AB amps utilize a series of transistors that each amplify a separate area, each of which being more efficient than class-A amplifiers. The larger efficiency of class-AB amplifiers also has two further benefits. Firstly, the necessary amount of heat sinking is minimized. Consequently class-AB amplifiers can be made lighter and smaller. For that reason, class-AB amps can be made cheaper than class-A amps. When the signal transitions between the two separate regions, though, some amount of distortion is being created, thereby class-AB amplifiers will not achieve the same audio fidelity as class-A amplifiers.
Class-D amplifiers are able to attain power efficiencies higher than 90% by using a switching transistor which is constantly being switched on and off and as a result the transistor itself does not dissipate any heat. The switching transistor, which is being controlled by a pulse-width modulator generates a high-frequency switching component which has to be removed from the amplified signal by utilizing a lowpass filter. Due to non-linearities of the pulse-width modulator and the switching transistor itself, class-D amps by nature have amongst the largest audio distortion of any audio amp.
Class-D amplifiers are able to achieve power efficiencies higher than 90% by making use of a switching transistor that is continually being switched on and off and as a result the transistor itself does not dissipate any heat. The on-off switching times of the transistor are being controlled by a pulse-with modulator (PWM). Usual switching frequencies are in the range of 300 kHz and 1 MHz. This high-frequency switching signal has to be removed from the amplified signal by a lowpass filter. Typically a straightforward first-order lowpass is being utilized. Both the pulse-width modulator and the transistor have non-linearities that result in class-D amplifiers having larger music distortion than other kinds of amps. More recent audio amps incorporate some type of means to reduce distortion. One method is to feed back the amplified audio signal to the input of the amplifier to compare with the original signal. The difference signal is then used in order to correct the switching stage and compensate for the nonlinearity. One type of audio amplifiers which uses this type of feedback is called "class-T" or "t amp". Class-T amplifiers feed back the high-level switching signal to the audio signal processor for comparison. These amplifiers have small music distortion and can be made extremely small.
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